KR20080096561A - Method and system for scheduling users based on user-determined ranks in a mimo system - Google Patents

Abstract

A method and a system for scheduling users based on user-determined ranks are provided to improve the communication efficiency in MIMO system. A rank selector(305) selects a rank to maximize the capacity of subscriber station(111). A CQI calculator(310) then calculates a CQI for each virtual antenna based on the selected rank. Pre-coding matrix selector(315) then selects a preferred pre-coding matrix based on the calculated CQIs. If multi-user mode is not set statically, multiple CQIs, their corresponding pre-coding vector identifiers, and the selected rank are included in the scheduling data. However, if multi-user mode is set statically, a maximum CQI, its corresponding pre-coding vector identifier, and the selected rank are included in the scheduling data. Scheduling data reporter(320) then reports the scheduling data to the base station providing service to subscriber station.

Description

TECHNICAL AND SYSTEM FOR SCHEDULING USERS BASED ON USER-DETERMINED RANKS IN A MIMO SYSTEM}

The present invention relates generally to wireless communication networks, and more particularly, to a method and system for scheduling a user based on a user determined rank in a multiple input / multiple output (MIMO) system.

Orthogonal Frequency Division Multiplexing (OFDM) is a multi-carrier transmission technique in which a user transmits through multiple orthogonal frequencies (or subcarriers). Orthogonal subcarriers are individually modulated and separated in frequency so as not to interfere with each other. This provides high spectral efficiency and resistance to multipath effects. In Orthogonal Frequency Division Multiple Access (OFDMA) systems, some subcarriers may be assigned to different users rather than a single user. Today, OFDM technology and OFDMA technology include wired transmission systems such as Asymmetric Digital Subscriber Line (ADSL), IEEE-802.11a / g (ie WiFi), IEEE-802.16 (e.g. WiMAX), digital audio. It is used in both wireless transmission systems such as digital audio broadcast (DAB), and digital video broadcast (DVB). This technology is also used for wireless digital audio and video broadcasting.

In a conventional OFDM network, a fixed data rate can be used and the amount of transmit power can be adjusted based on how far the user is from the transmitting node. Alternatively, data can always be transmitted at full power, but if the user is close to the transmitting node, use higher order modulation and weak code. On the other hand, if the user is far from the transmitting node, use lower order modulation and strong codes. In some OFDM networks, two antennas are used to transmit two data streams to one user, resulting in a double data rate. However, at the cell edge, the two data streams can interfere with each other so that a long backoff time is required for modulation and coding for successful communication. Thus, there is a need in the art for an improved method of communicating with users in a MIMO system.

In a wireless network comprising a plurality of subscriber stations and base stations capable of providing services to the subscriber stations, subscriber stations are provided. According to a preferred embodiment of the present invention, the subscriber station includes a rank selector and a scheduling data reporter. The rank selector may select a rank for the subscriber station. The rank may identify multiple antennas transmitting the data stream from the base station to the subscriber station. The scheduling data reporter may report scheduling data including the rank to the base station.

According to another embodiment of the present invention, a method for scheduling a user at a base station based on a user determined rank in a MIMO system is provided, the method comprising receiving scheduling data from each of a plurality of users. The scheduling data for each user includes at least one Channel Quality Indicator (CQI), rank, and preferred pre-coding matrix and vector. Users are scheduled based on the scheduling data.

According to another embodiment of the present invention, there is provided a method of communication between a transmitter and a receiver in a MIMO system, the method comprising receiving a frame from the transmitter at the receiver. The frame includes a plurality of codewords. Each codeword has a different Hybrid Automatic Repeat Request (HARQ) channel. The frame is processed using a HARQ message.

Prior to entering the following detailed description of the invention, it may be desirable to define the terms or phrases used throughout this specification: “include” and “comprise”. ", And their derivatives, mean unlimited inclusion; The term “or” encompasses the meaning of “and / or”; The term "each" means all of one or more subsets of distinct items; "Related" and "associated with", and derivatives thereof, include, within, interconnected, nested, nested, linked, combined, communicable, cooperating, interleaved, parallel, proximity included. Mean, constrained, equipped, having properties, and the like; The term "controller" means any device, system, or portion thereof that controls at least one operation, and such device may be implemented in hardware, firmware, or software, or any combination of two or more thereof. It will be appreciated that the functionality associated with any particular controller may be implemented centrally or distributed locally or remotely. Definitions of specific terms and phrases are provided throughout this specification, and those skilled in the art will, in many cases, if not most of them, apply such definitions to previous and subsequent uses of the terms and phrases in which they are defined. It should be understood.

BRIEF DESCRIPTION OF DRAWINGS For a more complete understanding of the invention, the following description is set forth in conjunction with the accompanying drawings, in which like reference characters designate the same parts.

1 is a diagram illustrating a wireless network capable of scheduling a user based on a user decision rank in a multiple input / output system according to an embodiment of the present invention;

2A and 2B illustrate an Orthogonal Frequency Division Multiple Access (OFDMA) transmitter and an Orthogonal Frequency Division Multiple Access receiver, respectively, according to an embodiment of the present invention;

3 illustrates one of the subscriber stations of FIG. 1 in accordance with an embodiment of the present invention;

4 is a detailed view of the modulator of FIG. 2A included in one of the base stations of FIG. 1 in accordance with one embodiment of the present invention;

5 is a flowchart illustrating a method of generating scheduling data in a subscriber station of FIG. 3 according to an embodiment of the present invention;

6 is a flowchart illustrating a method of scheduling a subscriber station based on a rank using the modulator of FIG. 4 according to an embodiment of the present invention; And

7 is a flow diagram illustrating a method of data communication from the transmitter of FIG. 2A to the receiver of FIG. 2B in accordance with an embodiment of the present invention.

 1-7 and various embodiments used to describe the principles of the invention described below in this patent application are merely exemplary and should not be construed as limiting the scope of the invention. Those skilled in the art will appreciate that the principles of the present invention may be implemented in any wireless network suitably configured.

1 illustrates a wireless network 100 capable of scheduling a user based on a user determined rank in a multiple input / output (MIMO) system according to an embodiment of the present invention. In the illustrated embodiment, the wireless network 100 includes a base station 101, a base station 102, and a base station 103. Base station 101 communicates with base station 102 and base station 103. Base station 101 also communicates with an Internet Protocol (IP) based network 130, such as the Internet, a private IP network, or other data network.

Base station 102 provides a wireless broadband connection to network 130 via base station 101 to a plurality of first subscriber stations in communication area 120 of base station 102. The plurality of first subscriber stations includes subscriber station 111 to subscriber station 116. In an example embodiment, the subscriber station 111 may be located in a small business (SB), the subscriber station 112 may be located in a large enterprise (E), and the subscriber station 113 may be a WiFi hotspot (HS). ), The subscriber station 114 may be located in the first house, the subscriber station 115 may be located in the second house, and the subscriber station 116 may be a mobile device (M).

Base station 103 provides a wireless broadband connection to the network through base station 101 to a plurality of second subscriber stations in communication area 125 of base station 103. The plurality of second subscriber stations includes a subscriber station 115 and a subscriber station 116. In alternative embodiments, base station 102 and base station 103 may not be indirectly through base station 101, but may be directly connected to the Internet using a fiber optic broadband, DSL, cable or wired broadband connection such as a T1 / E1 line. Can be.

In another embodiment, base station 101 may communicate with fewer or more base stations. Also, although only six base stations are shown in FIG. 1, it should be appreciated that the wireless network 100 can provide wireless broadband access to more than six subscriber stations. Note that subscriber station 115 and subscriber station 116 are at the edge of communication area 120 and communication area 125. Subscriber station 115 and subscriber station 116 communicate with both base station 102 and base station 103, respectively, and may be said to be operating in handoff mode, as is well known to those skilled in the art.

In an exemplary embodiment, the base stations 101-103 are connected to each other and subscriber stations 111-116 using the IEEE-802.16 wireless metropolitan area network standard, such as, for example, the IEEE-802.16e standard. ) To communicate with. However, in other embodiments, other wireless protocols may be used, such as, for example, the HIPERMAN wireless MAN standard. Base station 101 may communicate with base station 102 and base station 103 via direct line-of-sight or non-line-of-sight, depending on the technology used for wireless backhaul. Base station 102 and base station 103 may communicate with subscriber stations 111-116 over an invisible line, respectively, using OFDM and / or OFDMA techniques.

The base station 102 may provide a T1 level service to a subscriber station 112 associated with a large company, and may provide a partial T1 level service to a subscriber station 111 associated with a small company. Base station 102 may provide a wireless backhaul to a subscriber station 113 associated with a WiFi hotspot that may be located at an airport, cafe, hotel or university campus. The base station 102 may provide digital subscriber line (DSL) grade service to the subscriber stations 114-116.

Subscriber stations 111-116 may use a broadband connection to network 130 to access voice, data, video teleconferencing and / or other broadband // services. In an example embodiment, one or more of the subscriber stations 111-116 may be associated with an access point of a WiFi WLAN. Subscriber station 116 may be any one of a number of mobile devices, including wireless-capable laptop computers, personal data assistants (PDAs), notebooks, handheld devices, or other wireless-capable devices. Subscriber station 114 and subscriber station 115 may be, for example, a wireless-capable personal computer, laptop computer, gateway, or other device.

The dashed lines indicate the approximate range of the communicable area 120 and the communicable area 150 and are shown as approximate circles for illustration and description only. It is evident that the communicable areas associated with the base stations, such as the communicable area 120 and the communicable area 125, may have other forms, including irregular shapes, depending on the configuration of the base stations and changes in the wireless environment associated with natural and man-made obstacles. You should know

In addition, the coverage areas associated with the base stations may not be changed over time, but may be dynamic (expanded or reduced or shaped) by changes in the transmit power level of the base station and / or subscriber stations, weather conditions, and other factors. May change). In one embodiment, the radius of the coverage area of the base stations, such as the coverage area 120 and 150 of the base station 102 and the base station 103 may extend from less than 2 km to about 50 km from the base stations.

As is known in the art, base stations such as base station 101, base station 102, or base station 103 use directional antennas to support multiple sectors in the communicable area. In FIG. 1, the base station 102 and the base station 103 are shown as being approximately in the center of the communicable area 120 and the communicable area 125, respectively. In other embodiments, the directional antenna may be used by positioning the base station near the edge of the communicable area, eg, at the vertex of the conical or pear shaped communication area.

The connection from the base station 101 to the network 130 may comprise a broadband connection, such as a fiber optic line, to a server located in a central office or other operator point-of-presence (POP). The servers may provide communication to an Internet gateway for Internet protocol based communication and a public telephone network gateway for voice-based communication. In the case of voice-based communication in the form of VoIP, traffic can be delivered directly to the Internet gateway, not to a public telephone network gateway. The servers, the Internet gateway, and the public switched telephone network gateway are not shown in FIG. In another embodiment, the connection to the network 130 may be provided by other network nodes and equipment.

As described in more detail below, one or more of the subscriber stations 111-116 may determine a rank for themselves and report the rank to the base stations 101-103. In addition, one or more base stations 101-103 may be able to schedule the subscriber stations 111-116 in their communication area based on the ranks reported by the subscriber stations 111-116. Each rank may identify multiple layers equal to the number of virtual antennas for transmitting the data stream from the base stations 101-103 to the subscriber stations 111-116 reporting the rank. As described in more detail below, the antennas may be composed of virtual antennas. In addition, the base stations 101-103 and the subscriber stations 111-116 can perform communication with each other using a hybrid automatic repeat request (HARQ) message.

MIMO systems include, but are not limited to, diversity gain for fading, beamforming gain, spatial multiplexing of multiple data codewords for the same user, and spatial multiplexing of multiple data codewords for other users (SDMA). This gives additional freedom that can be used for various system performance improvements. In a wireless environment, such as wireless network 100, different subscriber stations 111-116 (or users) will have different channel types due to different power delay profiles, travel speeds, and the like. In addition, different users have different Signal-to-Interference-plus-Noise Ratios (SINRs) due to user location, shadow fading, and the like. Using the principles of the present invention, the additional degrees of freedom afforded by multiple antennas can be utilized on a per-user basis to improve system performance and capacity while maintaining appropriate overhead and system complexity. It utilizes the additional degrees of freedom afforded by the precoded multiple transmit user antennas to simultaneously schedule multiple users over the same OFDM user block (SDMA) or transmit multiple data codewords to the same user (SDM). Can be achieved by implementing a coding scheme.

If there are many users in cells 120 and 125, significant gains can be realized in system throughput by using a multi-user MIMO (MU-MIMO) scheme over a single-user MIMO (SU-MIMO) scheme. This is because multi-user MIMO uses multi-user diversity gain (MUDG) per codeword level. However, single-user MIMO can increase the maximum user data rate. This is particularly important because of the bursty nature of the actual traffic flow (as opposed to full buffer modeling). There are often few users in cell 120 and cell 125 with active buffers. Thus, a MIMO scheme that supports both multi-user and single-user schemes without increasing signaling overhead is useful. The single-user MIMO scheme has the advantage of easily utilizing the use of sequential interference cancellation (SIC) enhanced by CRC encoding for each codeword. As will be described in detail below, the base stations 101-103 may determine the timing of switching between multi-user MIMO and single-user MIMO by appropriate criteria.

2A shows an OFDMA transmitter 200. 2B shows an OFDMA receiver 250. The OFDMA transmitter 200 or the OFDMA receiver 25, or both, may be implemented in any of the base stations 101 through 103 of the wireless network 100. Similarly, OFDMA transmitter 200 or OFDMA receiver 250 or both may be implemented at either of subscriber stations 111 to 116 of wireless network 100.

The OFDMA transmitter 200 includes a modulator 205, a S-to-P converter 210, an IFFT block 215, a P-to-S converter 220, a cyclic preinterval. An add cyclic prefix block and up-converter (UC) 230. OFDMA receiver 250 includes down-converter (DC) 250, cyclic pre-interval removal block 260, serial-to-parallel (S-to-P) converter 265, FFT block 270, parallel-serial ( A P-to-S converter 275 and a demodulator 280. In one embodiment, the modulator 205 comprises a QAM modulator and the demodulator 280 comprises a QAM demodulator. It should be appreciated that the transmitter 200 and / or receiver 250 may include additional components not shown in FIGS. 2A and 2B without departing from the scope of the present invention.

At least some of the components of FIGS. 2A and 2B may be implemented in software, while other components may be implemented in configurable hardware or in a mixture of software and configurable hardware. In particular, it should be noted that the IFFT block 215 and the FFT block 270 of the present invention can be implemented with a configurable software algorithm. These blocks 215 and 270 may each have a corresponding size of N, and the value of N may vary depending on the implementation.

In addition, the present disclosure is directed to embodiments that implement fast Fourier transforms and inverse fast Fourier transforms, but this is merely to illustrate the scope of the present invention and should not be construed to limit the scope of the present disclosure. In an alternative embodiment of the present invention, it is obvious that the fast Fourier transform and the inverse fast Fourier transform functions can be easily replaced with the discrete Fourier transform (DFT) and the inverse discrete Fourier transform (IDFT) functions, respectively. For the DFT and IDFT functions, the N value can be any integer (eg, 1, 2, 3, 4, etc.), while for the FFT and IFFT functions, the N value is any integer that is a power of two (eg , 1, 2, 4, 8, 16, etc.).

In one embodiment OFDMA transmitter 200, modulator 205 receives a set of information bits and modulates the input bits to generate a sequence of frequency-domain modulation symbols. As described in detail below, modulator 250 modulates the input bits using modulation and coding that may be selected based on the rank determined by the receiver 250. Serial-to-parallel converter 210 converts (eg, demultiplexes) the serial symbols into parallel data, thereby generating N parallel symbol streams. (Where N is the magnitude of the IFFT / FFT used in transmitter 200 and receiver 250). IFFT block 215 then performs an IFFT operation on the N parallel symbol streams to produce a time-domain output signal. Parallel-to-serial converter 220 converts (eg, multiplexes) the parallel time-domain output symbols from IFFT block 215 to produce a serial time-domain signal. Then, the cyclic prefix section adding block 225 adds the cyclic prefix section to the time-domain signal.

Finally, the up-converter 230 up-converts the output of the cyclic prefix interval addition block 225 to an RF frequency, depending on whether the OFDMA transmitter 200 is implemented in the subscriber station or the base station, depending on the forward channel or the reverse direction. Send through the channel. The signal from the cyclic prefix interval adding block 225 is filtered at baseband and then converted to an RF frequency. The time-domain signal transmitted by the OFDMA transmitter 200 includes multiple overlapping sinusoidal signals corresponding to the transmitted data symbol.

The RF signal that reaches the OFDMA receiver 250 is received from the forward channel or the reverse channel depending on whether the OFDMA receiver 250 is implemented in the subscriber station or the base station. The OFDMA receiver 250 reverses the operation performed by the OFDMA transmitter 200. Down-converter 255 down-converts the received signal to baseband frequency, and cyclic pre-interval removal block 260 removes the cyclic pre-interval to generate a serial time-domain baseband signal. Serial-to-parallel converter 265 converts the time-domain baseband signal into a parallel time-domain signal. FFT block 270 then performs an FFT algorithm to generate N parallel frequency-domain signals. Parallel-to-serial converter 275 converts the parallel frequency-domain signal into a sequence of data symbols. Demodulator 280 then demodulates the symbols to recover the original input data stream.

3 shows a subscriber station 111 in accordance with one embodiment of the present invention. For this embodiment, the subscriber station 111 includes a rank selector 305, a channel quality indicator (CQI) calculator 310, a pre-coding matrix selector 315, and a scheduling data reporter 320. It should be appreciated that the subscriber station 111 may include additional components not shown in FIG. 3.

As described in detail below, the rank selector 305 may be operable to select a rank for the subscriber station 111 for use in the scheduling of the subscriber station 111 by a base station such as base station 102. The rank selector 305 may select a rank to maximize the capacity of the subscriber station 111. In one particular embodiment, the rank may be low rank or high rank. In another embodiment, the rank may be one of three or more ranks.

The channel quality indicator calculator 310 may calculate a channel quality indicator (CQI) for each codeword received from the virtual antenna of the transmitter 200 based on the rank calculated by the rank selector 305. The pre-coding matrix selector 315 may be operable to select a predetermined pre-coding matrix for the subscriber station 111. As described in detail below, the pre-coding matrix selector 315 may select one preferred pre-coding matrix from any set of possible pre-coding matrices for the subscriber station 111.

Each pre-coding matrix consists of a plurality of pre-coding vectors. In one embodiment, the channel quality indicator calculator 310 may calculate a channel quality indicator (CQI) for each vector of each matrix of the matrix set. The pre-coding matrix selector 315 may select a pre-coding matrix having the best channel quality indicator (CQI) value calculated by the channel quality indicator calculator 310.

The scheduling data reporter 320 may report the scheduling data to a base station such as the base station 102. The scheduling data is a rank selected by the rank selector 305, one or more channel quality indicators (CQI) calculated by the channel quality indicator calculator 310, and a preferred pre-coding selected by the pre-coding matrix selector 315. Contains matrices and vectors. In one embodiment, the scheduling data includes a value of each channel quality indicator calculated by the channel quality indicator calculator 310. In another embodiment, the scheduling data may identify a vector corresponding to the single channel quality indicator value, along with a single channel quality indicator value, such as the best channel quality indicator value calculated by the channel quality indicator calculator 310. It can contain a vector identifier. In another embodiment, the scheduling data includes channel quality indicator values for each vector in the preferred pre-coding matrix.

Rank selector 305 may be used to select a rank for subscriber station 111. This is because some subscriber stations 111-116 experience correlated fading, while other subscriber stations 111-116 in the same cell 120 or 125 may experience uncorrelated fading. The rank selector 305 may select a rank on a conventional basis. For example, the rank selector 305 may select a rank, such as once for each Transmission Time Interval (TTI) or once for each resource block (eg, channel quality indicator feedback rate). . Optionally, rank selector 305 may occasionally select a rank, such as once for each of a number of defined transmission time intervals or once for a number of defined resource blocks. For example, for certain embodiments, rank selector 305 may select a rank for each 100 transmission time intervals.

In an embodiment where the rank selector 305 operates to select between a low rank and a high rank, the rank selector 305 may select a rank according to a performance maximizing formula. For example, for certain embodiments, the performance maximizing formula is as follows.

log ₂ (1 + SINR_MRC) <Σ _i log ₂ (1 + SINR_MMSE _i ),

In the above inequality, SINR_MRC is the signal-to-interference noise ratio (SINR) after maximum ratio synthesis. This can be calculated according to the signal magnitude received from each virtual antenna, where SINR_MMSE is the signal-to-interference noise ratio after minimum mean squared error synthesis. Accordingly, SINR_MRC represents the MRC composite received signal from the strongest virtual antenna, and SINR_MMSEi represents the MMSE composite received signal from the i th virtual antenna (and any other processing, such as SIC, which the subscriber station 111 may perform). Indicates. In this embodiment, the rank selector 305 may select a high rank when the inequality is satisfied and a low rank when the inequality is not satisfied. The method does not exclude the optimal search for ranks that maximize capacity across all possible ranks.

Thus, the measurement SINR_MRC according to a single data stream without interference is compared with the sum of the measurements SINR_MMSE for the interfering data streams. Using this inequality, the rank selector 305 can determine which rank maximizes the capacity of the subscriber station 111 and select that rank. The selection of low rank corresponds to requesting the base station 102 to transmit to the subscriber station 111 via a single antenna, while the selection of high rank requests the base station 102 to transmit to the subscriber station 111 via all antennas. Corresponds to. In other embodiments in which the rank selector 305 operates to select three or more ranks, it will be appreciated that the selected rank corresponds to requesting a different number of antennas for transmission to the subscriber station 111.

Using the inequality defined above, weak users will be likely to select low ranks, while strong users will be likely to select high ranks, since the selected rank will depend heavily on the geometry. If the subscriber station 111 is capable of performing SIC or other similar processing, it is also essentially included in the measurements considered in the rank selection, further increasing the likelihood of selecting a high rank. In some embodiments, if the rank selector 305 selects a low rank, the subscriber station 111 may be serviced by a non-spatial multiplexing scheme.

In some embodiments, the scheduling data reporter 320 may explicitly or implicitly report the rank selected by the rank selector 305. For explicit rank selection reports, scheduling data reporter 320 explicitly provides the base station 102 with the selected rank. This is generally an efficient way to report rank selection. For example, if the rank is low or high, a single bit is sufficient for the scheduling data reporter 320 to explicitly provide the rank to the base station 102. In addition, for low rank, scheduling data reporter 320 may provide only a single channel quality indicator to base station 102.

For implicit rank selection reports, scheduling data reporter 320 may indicate that a particular beam will be switched off by base station 102 by providing a channel quality indicator value of zero for that beam. This is a simple method that does not require rank selection and additional signal processing. However, to use this approach, a channel quality indicator value must be provided for each beam.

4 details a modulator 205 of one of the base stations, such as base station 102, according to an embodiment of the present invention. The modulator 205 includes a controller 405, a user grouper 410, a scheduler 415, a plurality of adaptive modulation and coding blocks 420, and a plurality of pre-coding vector blocks 430. And a precoder 425 including a plurality of summers 435. As described below, the pre-coding vector block 430 can apply a pre-coding vector to the incoming signal, the pre-coding vector comprising a specific pre-coding matrix from the pre-coding matrices. .

The controller 405 may receive the scheduling data 440 from each of the plurality of subscriber stations 111-116 or users present in the coverage area of the base station 102. Also, the controller 405 may generate a group control signal 445 for the user grouping device 410 according to the scheduling data 440. The user control signal 445 may indicate which user has selected the same preferred pre-coding matrix.

User grouper 410 may receive stream 450 from each user and group control signal 445 from controller 405. User grouper 410 may group stream 450 into user group 455 according to who prefers the same pre-coding matrix as indicated by group control signal 445.

In addition, the controller 405 priority control signal 460 that can be used to identify which user group 455 has the highest priority and which users have the highest priority within the user group 455. Can be generated. The scheduler 415 may receive the user group 455 and the priority control signal 460 and select the highest priority stream 465 for scheduling in accordance with the priority control signal 460. The highest priority stream corresponds to the users of the highest priority in the highest priority user group 455, up to M, the maximum number corresponding to the maximum number of antennas. In addition, the scheduler 415 may generate a pre-coding matrix signal 470 that can provide or identify a preferred pre-coding matrix for the user group 455 that includes the highest priority stream 465. have.

In addition, the controller 405 can generate a plurality of modulation and coding (MC) control signals 475 that can each operate to identify the modulation and coding scheme for that highest priority stream 465. . Each AMC block 420 receives the MC control signal 475 and its highest priority stream 465 and assigns the modulation and coding identified by the MC control signal 475 to the highest priority stream 465. May be applied to generate coded stream 480.

Each of the pre-coding vector blocks 430 of the pre-coder 425 may receive one of the pre-coding matrix signal 470 and the coded stream 480. In addition, each pre-coding vector block 430 applies a pre-coding vector to the coded stream 480 from the pre-coding matrix identified or provided by the pre-coding matrix signal 470 to apply a plurality of pre-codings. Coded vector signal 485 may be generated. Each summer 435 receives the pre-coded vector signal 485 from the pre-coded vector block 430, and adds the pre-coded vector signal 485 to the pre-coder output signal ( 490).

Pre-coder 425 consists of a single pre-coder. For example, in one embodiment, the pre-coding vector block 430 may apply a pre-coding vector determined according to the following formula.

For embodiments of a particular embodiment, two transmit antennas (M = 2) and two possible user groups 455 (G = 2) may be provided. For this example, the pre-coder matrix set can be defined as follows.

For another specific example, four transmit antennas (M = 4) and two possible user groups 455 (G = 2) may be provided. For this example, the pre-coder matrix set can be defined as follows.

For the more general embodiment shown in FIG. 4, the pre-coder matrix set is defined as follows.

는 g 번째 프리-코딩 행렬이고,

은 이 세트에서 m번째 프리-코딩 벡터이다. 이러한 실시 예의 경우, 가입국(111)의 채널품질지시 계산기(310)는 세트 E에 각각의 행렬 내 각각의 벡터에 대한 채널품질 지시자 값을 계산할 수 있다. 적당한 G 값을 선택하고, 각각의 스케줄링 데이터 보고기(320)에 의해 보고된 스케줄링 데이터 내에 포함될 정보의 양을 결정함으로써, 피드백 오버헤드의 양을 기지국(102)에서의 스케줄링 유연성과 트레이드 오프(trade-off)될 수 있다. here,

Is the g th pre-coding matrix,

Is the m th pre-coding vector in this set. In this embodiment, the channel quality indication calculator 310 of the subscriber station 111 may calculate the channel quality indicator value for each vector in each matrix in set E. By selecting an appropriate G value and determining the amount of information to be included in the scheduling data reported by each scheduling data reporter 320, the amount of feedback overhead is traded with the scheduling flexibility at the base station 102. -off).

For example, for the greatest flexibility, the scheduling data may consist of each channel quality indicator value for each matrix in set E, which is the total GM channel quality indicator for each subscriber station 111-116. The value CQI can be obtained. For the lowest overhead, the scheduling data may include only the best channel quality indicator value and the corresponding vector identifier, which may use log2 (GM) bits per subscriber station 111-116 in addition to the actual channel quality indicator value. This embodiment can only support a limited SDMA because each user is scheduled to one particular beam. In addition, it supports transmit beamforming only if the user is scheduled on a time-frequency basis. In the case of a mixture of SDM and SDMA, the scheduling data may include M channel quality indicator values corresponding to the preferred pre-coding matrix selected by the pre-coding matrix selector 315. It will be appreciated that the scheduling data may constitute other suitable data depending on the desired settings of the overall system.

5 is a flowchart illustrating a method 500 of generating scheduling data in a subscriber station 111 according to an embodiment of the present invention.

First, the rank selector 305 selects a rank that can maximize the performance of the subscriber station 111 (step 505). The channel quality indication calculator 310 then calculates a channel quality indicator for each virtual antenna according to the selected rank (step 510). The pre-coding matrix selector 315 then selects a preferred pre-coding matrix according to the calculated channel quality indicators (step 515).

If the multi-user mode is not statically set (step 520), the multi-channel quality indicator, their corresponding pre-coding vector identifier and selected rank are included in the scheduling data (step 525). However, if the multi-user is statically set (step 520), the maximum channel quality indicator, its corresponding pre-coding vector identifier and the selected rank are included in the scheduling data (step 530). The scheduling data reporter 320 then reports the scheduling data to the base station 102 serving the subscriber station 111 (step 535).

In this way, the subscriber station 111 may request that the base station 102 transmit through a certain number of antennas in order to maximize the performance for the subscriber station 111. For example, subscriber station 111 may report a lower rank to request transmission from a single antenna to maximize power, or may request a higher rank to request transmission from multiple or all antennas, which may require a data rate. Increase. .

Thus, for this embodiment, the subscriber station 111 first selects the best channel quality indicator, as well as the pre-coder antenna identifier of the codeword to be decoded (i.e., the codeword cannot gain in the SIC when the MU-mode is running). Report. In MU-mode, this is the only codeword that can be scheduled to the subscriber station 111. In the SU-mode, the subscriber station 111 is one for each of the M code words. Report the M channel quality indicator values.

In another implementation, the subscriber station 111 only needs to report a single CQI, where all M codewords will use the same link adaptation scheme, and codewords are interleaved across the antennas so that all codewords obtain average capacity. do. All of these codewords can be independently CRC-coded and benefit from nonlinear SIC processing.

FIG. 6 is a flow chart illustrating a method 600 of scheduling subscriber stations 111-116 according to rank to a base station 102 including a modulator 205 shown in FIG. 4 in accordance with one embodiment of the present invention. First, controller 405 receives scheduling data 440 from a plurality of subscriber stations 111-116 or users (step 605). Base station 102 selects the best user according to a proportional process criterion or other suitable selection algorithm (step 610). If the selected user is a low-rank user, no further processing is required and ends. However, if the selected user is a high-rank user, the method continues.

If the base station 102 selects a single-user (SU) mode other than the multi-user (MU) mode (step 620), the base station 102 schedules the selected user (step 625). In an embodiment, the base station 102 may select the SU-mode or the MU-mode according to the request for increasing the maximum data rate or the request for increasing the total data rate. For certain embodiments, base station 102 may make this determination according to the number of active buffers and / or channel quality indicators reported by users.

If the base station 102 selects a MU-mode other than the SU-mode, the user grouper 410 may stream 450 according to the user's preferred pre-coding matrix as identified by the scheduling data 440. ) Are grouped into user groups 455 (step 630). The scheduler 415 then selects the highest priority group for the highest priority user of the highest priority group (step 635) and selects the highest priority stream 465 or codeword (step). 640). For a particular embodiment, the scheduler 415 may select the user who reported the highest priority for that codeword for the next available codeword. Any subsequent user reports on the complementing pre-coding index (for previously scheduled codewords) to be considered for scheduling. According to the design of the scheduler 415, the base station 102 may schedule up to M codewords of data independent of other users or the same user.

Each AMC block 420 applies modulation and coding to the selected codeword to generate a coded stream 480 (step 645). Pre-coder 425 applies pre-coding to coded stream 480 according to the preferred pre-coding matrix of the highest priority user group (step 650). As described above in connection with FIG. 2A, additional processing may be provided for the codeword (step 655). Base station 102 then transmits the processed codeword to the highest priority users or subscriber stations 111 to 116 within the selected group (step 660).

In this way, base station 102 schedules users to maximize system performance (fairness limitation greedy technique). The scheduler 415 knows that with a large enough buffer, the MU-mode can maximize system performance, and with fewer users, SU-mode can maximize system performance.

In addition, features of this implementation of the wireless network 100 include multiple sets of predetermined single pre-codings, multi-user diversity gains provided in the spatial domain by degrees of freedom in a single pre-coding selection, and the like. . In addition, through spatial feedback, the user can report preferred unit pre-coding (ie, preferred pre-coding matrix). Through overall feedback, the user can report channel quality indicators corresponding to every single pre-coding. To provide closed loop beamforming, the user may preferentially report the beam in a single preferred pre-coding (ie, the preferred pre-coding matrix as well as the preferred pre-coding vector).

In addition, using the spatial channel information fed back from the users, the base station 102 can select the associated single pre-coding. This approach can implement SDMA because multiple users can also be scheduled with the same time-frequency resource and different beams can be assigned to users. Since multiple codewords of a single user can be scheduled with the same time-frequency resource, this approach can implement SDM. If a single codeword of a single user is transmitted in a single beam, this approach also performs closed-loop beamforming.

7 is a flow chart illustrating a method 700 for transferring data from a transmitter 200, such as a base station 102, to a receiver 250, such as a subscriber station 111, in accordance with an embodiment of the present invention.

First, receiver 250 receives a frame from transmitter 200 (step 705). In this particular example, the frame includes two codewords, codeword1 and codeword2. However, the frame may include any suitable number of codewords without departing from the scope of the present invention. In addition, in this embodiment each codeword has its own HARQ channel.

The receiver 250 decodes codeword 1 corresponding to the strongest codeword included in the frame (step 710). The receiver then attempts to verify the accuracy of the decoded codeword 1 by checking the CRC for codeword 1 (step 715). If CRC1 is incorrect (step 715), receiver 250 sends a negative acknowledgment (NACK) message to transmitter 200 for all codewords (step 720). This is because, as codeword 1 is not successfully decoded, receiver 250 assumes codeword 2 which is weaker than codeword 1 and will not be decoded successfully. As soon as the transmitter 200 receives the negative acknowledgment message, it transmits the codewords of both codeword 1 and codeword 2 from the transmitter 200 to the receiver 250 via a stronger antenna for each using a HARQ message. (Step 725).

Once codeword 1 is confirmed by a successful CRC check (step 715), receiver 250 sends an acknowledgment (ACK) message for codeword 1 to transmitter 200 (step 730). Receiver 250 then deletes the reconstructed codeword 1 signal from the received frame (step 735).

Receiver 250 then decodes codeword 2 (step 740). Receiver 250 then attempts to verify the accuracy of decoded codeword 2 by performing a CRC check on codeword 2 (step 745). If CRC2 is incorrect (step 745), receiver 250 sends a negative acknowledgment message for codeword 2 to transmitter 200 (step 750). As soon as the transmitter 200 receives the negative acknowledgment message, it transmits a new codeword 1 (since the existing codeword 1 has already been successfully decoded) using the HARQ message and retransmits codeword 2 via a stronger antenna ( Step 755).

Once codeword 2 is confirmed by a successful CRC check (step 745), receiver 250 sends an acknowledgment message for codeword 2 to transmitter 200 (step 760). As soon as the transmitter 200 receives the acknowledgment message, it transmits two new codewords from the transmitter 200 to the receiver 250 (step 765).

In this way, HARQ messaging is used with multiple input / output systems to increase throughput. The use of HARQ messaging increases the efficiency by allowing codewords to be transmitted at the lowest possible power. In addition, if the first codeword is successfully encoded and the second codeword is not successfully encoded, the transmitter 200 does not need to retransmit the second codeword together with the first codeword. Because the new codeword is transmitted with the transmitted second codeword, resources are not wasted in duplicate transmissions.

Although the present invention has been described as a representative embodiment, various changes and modifications may be suggested to those skilled in the art. It is intended that the present invention cover such changes and modifications as fall within the scope of the appended claims.

Claims (25)

A subscriber station in a wireless network comprising a plurality of subscriber stations and a base station capable of providing services to the subscriber stations, A rank selector operative to select a rank for the subscriber station; And A scheduling data reporter operative to report scheduling data including the rank to the base station, And the rank is for identifying a plurality of antennas for transmitting a data stream from the base station to the subscriber station. The method of claim 1, wherein the rank selector, A subscriber station in a wireless network capable of selecting one of a low rank and a high rank as a rank for the subscriber station. The method of claim 2, The plurality of antennas for transmitting a data stream from the base station identified by the low rank to the subscriber station includes one antenna, The plurality of antennas for transmitting the data stream from the base station identified by the high rank to the subscriber station includes M antennas, and the M antennas include the maximum number of antennas available for data stream transmission from the base station. In a wireless network. The method of claim 1, wherein the rank selector, A subscriber station in a wireless network capable of selecting a rank once for each of a specified number of transmission time interval intervals (TTIs). The method of claim 1, wherein the rank selector, A subscriber station on a wireless network whose rank can be selected according to the formula for maximizing performance. The method of claim 5, wherein the maximum performance formula, In a wireless network that includes inequality log2 (1 + MRC) < Σ _i log 2 (1 + MMSEi), the rank selector selects a lower rank if the inequality is not satisfied and a higher rank is selected if the inequality is satisfied. Member States of The method of claim 1, And a channel quality indicator (CQI) calculator for calculating a channel quality indicator for each of a plurality of codewords received from each antenna of the base station based on the rank, And the scheduling data further comprises at least one channel quality indicator. The method of claim 1, Further comprising a pre-coding selector capable of selecting a preferred pre-coding matrix from the set of pre-coding matrices for the subscriber station, And the scheduling data further comprises the preferred pre-coding matrix. The method of claim 1, wherein the scheduling data reporter, Wireless capable of reporting scheduling data comprising a first data set if the base station is operating in a multi-user mode, and reporting scheduling data comprising a second data set if the base station is operating in a single-user mode Subscriber in the network. The method of claim 1, wherein the scheduling data reporter, A subscriber station in a wireless network capable of reporting scheduling data using either an explicit rank selection report or an implicit rank selection report. The method of claim 1, wherein the subscriber station, A subscriber station in a wireless network operable to decode frames received from a base station using a hybrid automatic repeat request (HARQ) message. A method for scheduling users at a base station according to a rank determined by a user in a multiple input / output system, Receiving scheduling data from each of the plurality of users; And Scheduling the users according to the scheduling data; And scheduling data for each user comprises at least one channel quality indicator, rank, and preferred pre-coding matrix. The method of claim 12, wherein the scheduling of the users according to the scheduling data comprises: Grouping the users into user groups, wherein each user group comprises grouping each user group that includes the same preferred pre-coding matrix. Way. The method of claim 13, wherein the scheduling of the users according to the scheduling data comprises: Selecting the highest priority user group; Selecting a specific number of highest priority users in the highest priority user group; And Scheduling the specific number of highest priority users in the highest priority user group. The method of claim 14, wherein the scheduling of the users according to the scheduling data comprises: Applying modulation and coding to codewords for each of the highest priority users. The method of claim 15, wherein the scheduling of the users according to the scheduling data comprises: Applying precoding to the modulated and coded codewords based on the preferred pre-coding matrix for the highest priority user group. The method of claim 12, And determining whether to operate in one of a multi-user mode and a single-user mode in accordance with the scheduling data. The method of claim 17, wherein the scheduling of the users according to the scheduling data comprises: And scheduling the best user when operating in a single-user mode. The method of claim 17, wherein the scheduling of the users according to the scheduling data comprises: Scheduling users at a base station when operating in a multi-user mode comprising scheduling users of the highest priority group that contain the same preferred pre-coding matrix. A method for performing communication between a transmitter and a receiver in a multiple input / output system, Receiving a frame from the transmitter at the receiver; And Processing the frame using a HARQ message; The frame includes a plurality of codewords, each codeword corresponding to a different HARQ channel. The method of claim 20, wherein the processing of the frame using a HARQ message comprises: Decoding a first codeword in the frame; Determining whether the decoded first codeword is correct; And And transmitting a negative acknowledgment for the plurality of codewords from the receiver to the transmitter if it is determined that the decoded first codeword is incorrect. 22. The method of claim 21, further comprising: receiving a next frame from the transmitter to the receiver in response to the negative acknowledgment of the plurality of codewords, from the transmitter to the receiver. How to. The method of claim 22, wherein when the frame includes two codewords, the process of processing the frame using the HARQ message includes: Sending an acknowledgment for the first codeword from the receiver to the transmitter if it is determined that the decoded first codeword is correct; Deleting the first codeword from the frame; Decoding a second codeword in the frame; Determining whether the decoded second codeword is correct; And If it is determined that the decoded second codeword is incorrect, sending a negative acknowledgment for the second codeword from the receiver to the transmitter. The method of claim 23, In response to the negative acknowledgment for the second codeword, the receiver receives a next sequence of frames from the transmitter, wherein the next sequence of frames includes the same second codeword as the first codeword of the next sequence A method for performing communication between a transmitter and a receiver. The method of claim 24, The process of processing a frame using a HARQ message, If it is determined that the decoded second codeword is correct, sending an acknowledgment for the second codeword from the receiver to the transmitter; And In response to the acknowledgment of the second codeword, receiving at the receiver a frame of the next order from the transmitter, And wherein the next sequence of frames includes a first codeword of a next sequence and a second codeword of a next sequence.

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